Arena polish: in-run HUD, no free loot, retire-with-winnings

- HUD arena status (top center): live wave number and run gold,
  driven by GameState signals, torn down cleanly on HUD.reset()
- Free floor weapons removed: the initial sword/shield spawn is gone
  and manually placed level.tscn weapons are deleted server-side at
  init. Gear now only enters play via the armory or enemy drops.
- Retire to Camp: new escape-menu button (shown only while alive in
  an active run) banks 100% of run gold and keeps all gear - the
  counterweight to death's 10% settlement. Exit Game and window close
  also bank winnings before quitting.
- CLAUDE.md rewritten for the gladiator arena era: core loop,
  autoloads, economy API, RPC patterns, verification workflow.

level/scripts/game_state.gd

@@ -39,6 +39,11 @@ signal loadout_changed(loadout: Dictionary)
 func _ready() -> void:
 	load_save()
 
+func _notification(what: int) -> void:
+	# Closing the window mid-run counts as walking out alive - bank the winnings
+	if what == NOTIFICATION_WM_CLOSE_REQUEST and run_active:
+		retire_run()
+
 # --- Persistence ---------------------------------------------------------
 
 func load_save() -> void:
@@ -186,6 +191,31 @@ func end_run() -> Dictionary:
 	run_ended.emit(last_run_stats)
 	return last_run_stats
 
+## Walk out of the arena alive: bank 100% of run gold, keep all gear.
+## The reward for retiring instead of dying (death only keeps 10%).
+func retire_run() -> Dictionary:
+	if not run_active:
+		return last_run_stats
+	run_active = false
+
+	last_run_stats = {
+		"waves": current_wave,
+		"kills": kills_this_run,
+		"time": get_run_time(),
+		"gold_earned": run_gold,
+		"total_value": get_total_value(),
+		"kept": banked_gold + run_gold,
+		"retired": true,
+	}
+
+	banked_gold += run_gold
+	run_gold = 0
+	gold_changed.emit(banked_gold)
+	run_gold_changed.emit(run_gold)
+	save_game()
+	run_ended.emit(last_run_stats)
+	return last_run_stats
+
 # --- Multiplayer crediting (server -> owning peer) ------------------------
 # GameState is an autoload, so it exists at the same path on every peer with
 # the server (peer 1) as its multiplayer authority. The server decides who